Thanks to Skillshare for sponsoring this episode. [♩INTRO].

Imagine you’re sitting in a movie theater chomping down on popcorn, and the newest blockbuster is just about to start. To get ready for the action, the theater decides it’s time to dim the lights.

This might seem like a simple adjustment, but inside those light bulbs, there’s actually a small rave going on. Because although you’ll probably never notice it, dimmer switches are basically strobe lights and are way cooler than you might have thought. Until the 1950s, dimmer switches used to work how you might expect:.

They limited the amount of energy getting to a light by using some of it up. They did this by running the electricity through a resistor which, like the name suggests, resists the flow of electrical current. That burned off the extra power before it reached the bulb and made the light fainter.

But it also wasted lots of energy, and generated a lot of heat. Then, in 1959, an inventor named Joel Spira came along and changed the game when he made the first dimmer switch for homes. And while there are now multiple kinds of them, most use Spira’s original strategy:.

They manipulate alternating current, also known as AC. AC is what’s supplied by the electrical sockets in your walls, and it’s referred to as alternating because the current periodically changes direction. It might not sound that efficient, but the constant shifting makes it easier for the current to be transformed from the high voltages made in power plants to what’s needed for your hair dryer.

Countries use different standards for the frequency at which it switches, but in the U. S., it reverses 120 times a second. Normally, that means your wall lights flash just as often.

But dimmer switches change that. See, when the current reverses direction, the dimmer switch actually turns off the light. Then it stays off for a tiny fraction of a second.

When you lower the slider on the wall, you’re telling the switch to keep the light off a little bit longer. And with longer gaps in between flashes, the light looks dimmer. By staying off for more of each AC cycle, the bulb gets less energy all without the extra heat loss the old designs had.

But clearly, it’s not like you notice all this flashing. If you did, it would give mood lighting a whole different mood. Some of this depends on the lightbulb.

Some older bulbs that use filament don't have enough time to cool down in between flashes, which helps the glow appear constant. But more generally, you don’t notice the switching because, no matter how dim the light gets, it still crosses what’s called the flicker fusion threshold. This is the frequency at which lights need to flash for the average person to see them as continuous.

It’s the same phenomenon the affects the number of frames per second movies need to play at to look smooth. Things like your age and how tired you are can affect your threshold, but in general, dimmer switches always stay above the limit, so you never notice them turning on and off. So if you’re ever in the mood for a party, just get your dimmer switches ready.

They’re basically the most chill strobe light you’ll ever find. We care a lot about lighting here on the SciShow set. It’s what makes our hosts and our green screen look so good.

If you’ve ever wanted to learn more about studio lighting, but didn’t know where to start, Skillshare has a great class about it, taught by cinematographer Matt Workman. He teaches you the basics of lighting a seamless paper background, which is a pretty cheap and easy way to get some professional-looking shots. And if lighting isn’t your thing, Skillshare has more than 20,000 other classes about everything from cooking to music, so there’s a lot to explore.

Right now, Skillshare is offering SciShow viewers 2 months of unlimited access to all of their classes for free! So whether it’s cinematography or something else, you can pick up a new skill all while supporting SciShow. Just follow the link in the description to check it out for yourself! [♩OUTRO].